Artificial silk



1934- H. T. CLARKE r-:r m. 1,969,454.

ARTIFICIAL SILK Original Filed March 4, 1931 Patented Aug. 7, 1934 v UNITED STATES PATENT OFFICE ARTIFICIAL SILK Hans T. Clarke,-New York, and Carl J. Malm, Rochester, N. Y., assignors to Eastman Kodak Company, Rochester, N. Y., a corporation of New York 6 Claims.

This invention relates to a process of producing filaments or artificial silk from cellulose acetatepropionate containing 10%-30% and preferably about 15% of propionyl groups (figured as per cent of the entire ester) and to the silk so produced. This application is a division of our application Serial No. 520,149, filed March 4, 1931, and a continuation-in-part of our application Serial No. 179,177, filed March 28, 1927.

It has been known heretofore to make artificial silk from regenerated cellulose such as viscose or from cellulose acetate but those materials have certain disadvantages which are overcome in the employment of a cellulose acetate-propionate, such as we employ for the making of artificial silk.

Artificial silk which is produced at present from materials other than that which the applicant employs has a reputation of being none too resistant to washing materials. As a consequence, in many cases because of the lack of resistance of present day artificial silk to washing, the consuming public is demanding cotton garments and fabrics instead of those of artificial silk which obviously have a much better initial appearance and a. smoother feel to the skin than materials of untreated cotton. In cases where untreated cotton is-unsuitable, such as where a silky appearance is desired, the consuming public is turning to the more expensive silk instead of purchasing an artificial silk, the luster and life of which is short.

We have found that artificial silk made from cellulose acetate-propionate containing more than 10% and preferably about 15% of propionyl groups (figured as per cent of the entire ester) in distinction to artificial silk of cellulose acetate, for instance, is resistant to the action of boiling water, soaps and commonly employed washing alkalies.

For example, if a cellulose acetate fabric be boiled in soapy water (or clear water, for that matter) the fabric will be delustered, to a degree depending on the severity of the conditions. On the other hand, a cellulose acetate-proprionate fabric such as we have discovered may be treated under similar severe conditions without having its beauty and brilliance impaired. We have made possible, wash garments of artificial silk whose life and beauty will not be impaired by laundering operations, even as severe as those carried out'iti' commercial laundries.

Previously known artificial silk when wetted is greatly reduced in strength, so that in the manufacture of the same the laundering of the finished product or even dampening due to perspiration or rainfall greatly weakens the threads so that breaking with accompanying unraveling is common in this type of material. We have found that the threads of artificial silk made from cellulose acetate propionate of a propionyl content greater than 10% (figured as percent of the entire ester) have a wet strength considerably more than that of ordinary artificial silk so that the danger of breaking of threads is reduced to a minimum. As a consequence, garments made of our artificial silk may be .handled when wet without the great danger of breaking of thread with subsequent unraveling and ruin of the garment. This feature is especially valuable in goods of a fine, lacy nature.

Another advantage of employing cellulose acetate-propionate of more than 10% propionyl content is that a greater variety of solvents may be employed in the production of the filaments than is possible with cellulose acetate.

This allows the selection of the solvent best suited for the filamenting of the cellulose acetatepropionate. For example, acetoneis the solvent commonly employed for filamenting cellulose acetate. However, in the case of cellulose acetate-propionate of more than 20% propionyl content (figured as percent of the entire ester), we have found ethylene chloride to be eminently suitable for the filamenting of that particular ester. Ethylene chloride is less expensive than acetone and also gives a more brilliant product, due, probably, to the fact that it is not afiected by moisture so that any tendency toward dullness from the presence of moisture is .eliminated. Also, any moisture which may be present would distill azeotropically with the ethylene chloride upon filamenting in the dry-spinning or evaporating process which we prefer to employ in the present case.

As is well known in the cellulose acetate industry, the cellulose acetate tobe suitable for products such as filaments must be hydrolyzed usually to an acetyl content of about 38-40%. It is also well known that the trior fully esterified ose exhibit a greater resistance to wetting than esters which have been hydrolyzed. This naturally follows as it is common knowledge that, other things being equal, the more hydroxyl groups in a molecule, the more compatible the molecule becomes to water. In our present invention either the fully esterified cellulose acetate-propionate or the hydrolyzed ester may be employed to produce filaments.

For example, if a filament'is desired which is g highly resistant to wetting, the fully esterified ester is employed. Obviously, such filaments will also be resistant to a certain extent to dye baths and, consequently, to obtain a product which is to be dyed a partially hydrolyzed ester is more suitable although by no means necessary.

In cases where a mixture of light threads is desired in a dark fabric, some threads of the fully esterified ester may be incorporated in a fabric of the partially hydrolyzed ester and the whole, upon being subjected to a dye bath, will give a dark fabric having light threads therein. Obviously, a light fabric having dark threads incorporated therein may be made by using the fully esterified ester forthe body of thefabric and incorporating threads of the partially hydrolyzed ester therein. Various other decorative and useful effects may likewise be produced.

The accompanying diagrammatic drawing i1- lustrates by way of example one form of apparatus in which our process may be embodied.

Figure 1 is a. side elevation of a unit of 'a spinning machine which may be employed in producing artificial silk according to our process.

Figure 2 is a section at right angles to Figure 1 taken through the line 2-2 of Figure 1. 1 represents the pipe or manifold through which the cellulose ester solution or dope may be supplied by means of valve 2 and pump 3 to the filamenting apparatus. The dope or solution passes through a candle filter 4 which is enclosed in a chamber 5 heated by means of hot water coils 6 or other well known heating means as described and claimed in Stone application Serial No. 560,191, filed Aug. 29, 1931. This chamber 5 is separated from the spinning cabinet 9 by a partition which may be wellinsulated if desired. In fact it is preferred to insulate the entire chamber 5.

If the temperature at which it is desired to keep the candle filter should be considered unimportant, obviously the hot water coils may be omitted and if some heat is desired around the candle filter, the heated air from below may be allowed to surround it. It is, however, desirable as described in the above Stone application to main-, tain the candle filter at a temperature somewhat above that of the air of the spinning chamber. The candle filter 4 is connected with a spinnerette 7 to form the dope as it comes through the candle filter intofilaments of a'desired size and deliver them into the heated air present in the spinning cabinet 9. The cabinet 9, is provided withan air inlet 19 at its lower end in which is located a steam pipe 18 with heat dissipating fins 17, which heats the incoming air. Obviously other means of'heating the incoming air than that shown may be employed, the steam pipe with heat dissipating means located in the bottom of the cabinet is shown merely as an example of one means which may be employed to heat the incoming air. The solvent laden air in the upper portion of the cabinet may be removed through the outlet 8 which leads to a solvent rethe guide 14, to assure uniform winding of the thread. The spinning pot or bobbin is rotated by means of a motor, a tape or a belt drive or any other suitable device which may also be employed for operating the guide -14 in any suitable manner 30 desired. .A waste roll 13 is provided below the draw roll 12 to collect any threads which might drop from the draw roll.

- It is to be understood that instead of a spinning pot and roll winding, any other method such as cap spinning, may be employed to collect the thread after its formation. The above example illustrates one means of producing artificial silk filaments from a cellulose acetate-propionate dope. Instead of evaporative spinning, other methods of filamenting the dope hydrolyzed (in accordance with the Malm and Fletcher application Serial No. 551,546 filed July 17, 1931) for about 120 hours at about F. and which has a propionyl content of about 15% (figured as percent of the entire ester) was dissolved in acetone to form a 26% solution of the ester, the solution having a viscosity of 135,000 centipoises. This solution was run through the candle filter 4 and the spinnerette 7, the candle 1 filter being kept constantly at a temperature of. about 65 C. The temperature at the bottom of the cabinet was maintained at 58 C. by incoming heated air and the heating coils and the withdrawal temperature of the solvent-laden air was found to be 48-53" C. when air was passed through the cabinet at the rate of 20 cu. ft. per minute. A thread of 150 denier was thus formed. Obviously, if the threads are larger it will be. advantageous to pass air through the cabinet at a more rapid rate.

The thread produced was found to have a wet strength of .89 gms. per denier as compared with a wet strength of .65-.75 gms. per denier for cellulose acetatean increase of 20 to 40%. It was found to retain its luster and brilliance upon intense boiling and when treated with aqueous solutions of soap and alkalies in much greater concentrations than ordinarily employed inlaundering operations.

Various suitable solvents may be employed instead of acetone in the production of artificial silk from cellulose acetate-propionate'of more than 10% propionyl content. As mentioned previously, ethylene chloride is particularly suitable for the production of lustrous threads according to our process. Also, other solvents such, for example, as acetone-alcohol mixtures or ethylene chloride-alcohol or, for that matter, any yolatile solvent in which the cellulose acetate-propionate is soluble may be employed for filamenting it. If a composition of different evaporation Thar acteristics is desired, obviously a higher" boiling solvent 'such as'one of the higher alcohols may be added to the low boiling solvent. 1 a

Obviously, in the foregoing 'example, the f esterified' ester may beemployed instead of the I partially hydrolyzed ester and, as pointed out previously, the filaments formed will be more re-' sistant to water and dyes than those formed from the cellulose acetate-propionate which has been partially hydrolyzed. 1

As pointed out in our co-pending application No. 528,966 various plasticizers such as triphenylor tricresyl-phosphate may be incorporated with the cellulose acetate-propionate which we employ for'making artificial silk when the threads of a more pliable nature are desired.

Other obvious modifications of the present process will be apparent to those skilled in the art and are within the contemplation of this invention.

For example other lower mixed esters of cellulose such as cellulose acetate butyrate, having a content of the high acyl group such as butyryl corresponding to the propionyl content of the cellulose acetate-propionates referred to herein, may be employed to make artificial silk in the same manner as described herein with reference to cellulose acetate-propionate- We claim as our invention:

1. Anartificial silk comprising filaments of cellulose acetate-propionate containing acetyl groups and having a propionyl content of at least 10%.

2. An artificial silk comprising filaments of 5.- An artificial silk comprising filaments of partially hydrolyzed cellulose acetate-propionate containing acetyl groups and having a propionylcontent of at least 10%.

6. An artificial silk comprising filaments oi cellulose acetate proprionate containing acetyl groups and having a propionyl content of 10-30%.

, HANS T. CLARKE.

CARL J. MALM. 

